This invention relates to an injection molding unit which has at least one driving cylinder for inserting the unit in or removing it from an injection mold assembly received in a mold closing unit of an injection molding machine. The injection molding unit further has a hydraulic injection cylinder for performing injection strokes of a feed screw which is axially displaceably received in the plasticizing cylinder of the injection molding unit and which is provided with a drive for rotating the same. The injection molding unit also has a carrier block which cooperates with the plasticizing cylinder and which is axially displaceable on stationary columns. The carrier block has a supply device for the synthetic material as well as a central bore into which the plasticizing cylinder projects in a form-fitting manner and is axially immobilized therein. The injection molding unit further comprises a coupling device which includes radially slidable locking bolts for a centrally controllable replacement of the plasticizing cylinder.
In a known injection molding unit of the above-outlined type, as disclosed, for example, in German Offenlegungsschrift (non-examined published patent application) No. 3,229,223, the plasticizing cylinder and the carrier block which is provided with a trickle chute as well as a supply device for the synthetic material, constitute a structural unit. Except for the supply device for the synthetic material which may be removed from the structural unit, the latter is, as a whole, intended and adapted for replacement in the injection molding machine. In the working position the unit is, with the aid of the coupling device, connected to the remaining component assembly of the injection molding unit. The diametrically arranged slidable locking bolts of the coupling device which effect the above-noted connection, are radially slidably supported in the housing of the remaining component assembly of the injection molding unit and engage, with cooperating oblique surfaces, behind a radial terminal flange of the carrier block. Consequently, a replacement of the plasticizing cylinder is possible only by disconnecting and moving away the entire structural unit formed of the plasticizing cylinder and the carrier block, from the remaining component assembly of the injection molding unit. For this purpose, the locking bolts of the coupling device are moved into their withdrawn, releasing position when the structural unit is secured to the hoist mechanism which performs the removing operation.
Since a synchronous engagement with the locking bolts - which are driven by separate hydraulic devices and which function as wedges - is inherently not possible, the locking bolts have, during the coupling procedure, a de-centering effect on the structural unit formed of the plasticizing cylinder and the carrier block. Furthermore, the new injection techniques increasingly require longer plasticizing cylinders in which even slight centering errors result in significant positioning errors at the nozzle.